Catherine McGeoch, a computer scientist at Amherst College, in Massachusetts, was hired as a consultant by D-Wave to help set up performance tests on the 512-qubit machine for a consortium of Google, NASA, and the Universities Space Research Association. in September 2012.
Media reports focused on the fact that D-Wave’s machine had performed 3600 times as fast as commercial software by IBM. But such reporting overlooked McGeoch’s own warnings that the tests had shown only how D-Wave’s special-purpose machine could beat general-purpose software. The tests had not pitted D-Wave’s machines against the best specialized classical computing algorithms.
D-Wave’s machines have not yet demonstrated that they can perform significantly better than classical computing algorithms as problems become bigger. Daniel Lidar, scientific director of the Lockheed Martin Quantum Computing Center at USC, says D-Wave’s machines might eventually reach that point—as long as D-Wave takes the problem of decoherence and error correction more seriously.
D-Wave has gained some support from independent scientific studies that show its machines use both superposition and entanglement. The latter phenomenon allows several qubits to share the same quantum state, connecting them even across great distances.
But the company has remained mired in controversy by ignoring the problem of decoherence—the loss of a qubit’s quantum state, which causes errors in quantum computing. “They conjecture you don’t need much coherence to get good performance,” says John Martinis, a professor of physics at the University of California, Santa Barbara. “All the rest of the scientific community thinks you need to start with coherence in the qubits and then scale up.”
The debate continues to evolve as more independent researchers study D-Wave’s machines. Lockheed Martin has been particularly generous in making its machine available to researchers, says Matthias Troyer, a computational physicist at ETH Zurich. (Troyer presented preliminary results at the 2013 Microsoft Research Faculty Summit suggesting that D-Wave’s 512-qubit machine still falls short of the best classical computing algorithms.)
Google’s coalition also plans to let academic researchers use its D-Wave machine.
“The change we have seen in the past years is that by having access to the machines that Lockheed Martin leased from D-Wave, we can engage with the scientists and engineers at D-Wave on a scientific level,” Troyer says.